The regulation of gene expression is vital for healthy development and physiology, and many diseases are caused by or associated with changes in gene expression. In the past decade, a tremendous amount of information has been gathered regarding transcriptional control by transcription factors that bind directly to regulatory DNA sequences in or around their target genes. In addition, microRNAs that control gene expression post-transcriptionally have been studied extensively. However, functional and biochemical information about the vast majority of RNA binding proteins has been lacking despite clear evidence of their importance in development and disease. A major factor contributing to our limited understanding of post- transcriptional control by RNA binding proteins is a shortage of appropriate technologies that start with an important mRNA, for instance corresponding to a disease gene of interest, and identify the RNA binding proteins with which this mRNA interacts. In the proposed project, we will develop a novel, high-throughput method for the detection and identification of RNA-protein interactions. We have provisionally named this technology RNA-associated protein interaction detection (RAPID). RAPID is based on translation and mimics endogenous RNA binding protein activity. We will first develop and apply RAPID to RNA-protein interactions in the nematode Caenorhabditis elegans because it provides a highly suitable model for further in vivo studies, and because we have clone resources such as the ORFeome available, which contains numerous full-length RNA binding protein-encoding clones. Successful completion of this project will provide the research community with a novel and broadly applicable method to detect RNA-protein interactions in an unbiased and high-throughput manner. We envision applying RAPID to the genome-scale detection of such interactions to further our understanding of complex gene regulatory networks. The methodology and RNA binding protein resource that we will develop for C. elegans will provide an important blueprint for the creation of similar resources in other model organisms and humans.